The use of wing-beat frequency for insect detection prior to the instant invention has relied on wing-beat modulation of either sunlight or light from a Light Emitting Diode (LED), halogen lamp, or other broadband artificial light source. For example, Reed et al. describe using stroboscopic photography to study the wing-beat frequency as a mechanism of identifying insect species by photographing insect wings in motion through the use of flashing lights synchronized with the wings (S. C. Reed, C. M. Williams, and L. E. Chadwick, “Frequency of wing-beat as a character for separating species races and geographic varieties of drosophila,” Genetics 27, p. 349, May 1942). Also, Richards (“Photoelectric cell observations of insects in flight,” Nature Jan. 15, 1995, pp. 128-129) reported bursts of signal when viewing the Sun with a photocell that he ascribed to wing-beat modulations by flying insects. Another relatively early paper describing an optical technique to study insect wing beats is that of D. M. Unwin and C. P. Ellington, “An optical tachometer for measurement of the wing-beat frequency of free-flying insects,” J. Exp. Biol. 82, pp. 377-378, 1979. Their paper describes an electronic circuit for a system using a photodiode to detect wing-beat frequency using wing-beat modulated ambient light (i.e., sunlight).
Moore et al. (A. Moore, J. R. Miller, B. E. Tabashnik, and S. H. Gage, “Automated identification of flying insects by analysis of wing-beat frequencies,” J. Economic Entomology 79(6), pp. 1703-1706, 1986) describe the use of a microcomputer-based instrument to record and analyze flight movements of individual mosquitoes (i.e., Aedes aegypti (L.) and A. triseriatus) flying through a light beam. Moore and Miller (“Automated identification of optically sensed Aphid (Homoptera: Aphidae) wing-beat waveforms,” Ann. Entomological Society of America, 95, pp. 1-8, 2002) use an optical sensor to make digital recordings of wing-beat waveforms for the five most common aphids found on Guam. In this study the insects were housed in a clear plastic jar with the detector placed on one side and a halogen lamp on the other side as the source. The distance between the detector and source was 0.5 m. These articles appear to be the basis of the ‘Optical Flying Insect Detection and Identification System’ (OFIDIS) for automated insect species detection marketed by Qubit Systems Inc. (http://www.qubitsystems.com/). The User's Manual for the OFIDIS system is available online at http://frontpage2000.family-net.org/amoore/LibDocs/ofidis_document_library.htm. This manual is dated Jul. 6, 2001, and provides experimental results for the pomace fly (Drosophila melanogaster), red lily leaf beetle (Liliocerus lilii) and pink-spotted lay beetle (Coleomegilla maculata). The optical source for OFIDIS can be either the Sun, in which case the detector is oriented to look upward, or an artificial source such as an LED or halogen lamp, in which case the light source is pointed at the detector and the signal is created by insects modulating the transmitted light as they fly between the lamp and the detector. The lamp-based method uses the detection of transmitted light as an insect flies through a small region between the transmitting lamp and a detector (i.e., it is a transmitted-light measurement, not a scattered-light measurement). Sable Systems International sell the iFlySpy™ system, which uses a solar cell detector to detect wing-beat modulated sunlight in a manner very similar to that of the OFIDIS system (http://www.sablesys.com/iflyspy.html). Neither of these measurement schemes (Sun or LED) allow remote detection of insects in a horizontal-viewing mode with significant standoff distances between the measurement region and the sensor (i.e., >5 m, preferably tens of meters).
Anti personnel landmines kill approximately 15,000-20,000 people each year in roughly 90 countries (MacDonald et al., “Alternatives for landmine detection” (RAND Corp., 2003). Current detection methods for landmines include sweeping hand held metal detectors over suspected mine fields. However, this method results in high false alarm rates due to the inability to differentiate between landmines and other metallic objects and cannot detect plastic and plastic-like materials also used in landmines.
Active research in land mine detection includes electromagnetic induction, infrared and hyperspectral imaging, electrical impedance tomography, ground penetrating radar, electrochemical methods, and biological methods. The most common type of biological detection uses a trained dog and a handler. The dog is trained to detect the odor associated with the explosive contained in the landmine and then alert the handler. To accomplish this, the team must work in the mine field, placing both the dog and handler at risk.
A recently demonstrated biological detection technique by Bromenshenk et al. uses honeybees to locate buried landmines and explosives through the honeybee's sense of smell and their natural foraging behavior (Smith et al., “Volatile and semi-volatile organic compounds in beehive atmospheres” In Honey Bees: Estimating the Environmental Impact of Chemicals. Taylor and Francis, London and New York. 2:12-41, DeVillers, J. and M-H Pham-Delegue. Eds., 2002 ; Bromenshenk et al., Biological systems Alternatives for Landmine Detection, RAND Science and Technology Institute for Office of Science and Technology Policy Report, Arlington, Va. Appendix S, Eds. J. MacDonald et al. 2003; Bromenshenk et al., “Can Honey Bees Assist in Area Reduction and Landmine Detection?”, Journal of Mine Action Vol. 7.3, 2003; Bromenshenk et al., 2004 , Technical Report-Study/Services, CDRL DI-MISC-80598A, for Joint Chiefs of Staff, 2004 ). The honeybee conditioning is accomplished by adding trace amounts of the major chemical components of the explosive into a feeder. The honeybees are thus conditioned to associate the chemical smell with food and when the honeybees are released over a mine field, they will pause over the landmines as they forage for food. Trained honeybees were able to detect vapor levels higher than 50 parts per trillion (pptr) of 2,4 dinitrotoulene (2,4-DNT) mixed in sand (Bromenshenk et al., “Can Honey Bees Assist in Area Reduction and Landmine Detection?”, Journal of Mine Action Vol. 7.3, 2003).
The demonstrated ability of honeybees to detect explosives has led to a need for methods to remotely detect the presence and dwell time of honeybees in flight. Bender et al. (“Tracking Honey Bees Using Lidar (Light Detection and Ranging) Technology,” Sandia Report SAND2003-0184 (2003), Sandia National Laboratory, Albuquerque, N.Mex. 87185) pointed an existing atmospheric lidar system horizontally over a bee hive and demonstrated that they could see bees at a range of hundreds of meters. They operated in a vegetation-free environment and avoided letting the laser beam hit any object other than free-flying bees. The lidar instrument was aimed directly over a beehive where there was a high density of bees. However, this system was not tested with low honeybee density away from the beehive.
The prior art techniques discussed above cannot be used easily or effectively for measuring insect density over a region, such as an area suspected to contain explosives. Regarding the sunlight-based system, the Sun is rarely in a location so as to provide effective horizontal viewing (as opposed to detecting insects overhead). Regarding the LED- or lamp-based transmission system, the insects are only detected when they fly through a small sample region defined by the transmit-receive module and thus does not facilitate remote detection, such as of a potentially dangerous region. Regarding the direct-detection lidar systems, bee detection is complicated by the inability to distinguish between backscattered signals from bees and vegetation or other objects.
The following paragraphs describe these previous systems in more detail.